The present invention relates generally to automotive lighting assemblies. Specifically, the present invention relates to a testing apparatus and a method for checking leaks in glass-based light bulbs in automotive lighting assemblies.
One of the main components of an automotive lighting assembly is the light source. In many automotive lighting assemblies, the light source is a partially evacuated (about 0.6 atmosphere) glass-based light bulb having one or more filaments housed therein. A partial vacuum is necessary because the presence of too much oxygen within the light bulb oxidizes the filaments. Oxidation causes an electrical short in the filament, which in turn causes the filament to fail and the light bulb to become inoperable.
Light bulbs may be manually or automatically inserted into a variety of socket subassemblies and then assembled into a larger primary lighting assembly, such as, for example, automotive headlamp assemblies or traffic light assemblies. Socket subassemblies typically comprise a female receptacle into which the bulb is inserted to make an electrical connection and an electrical jack for connecting the bulb and socket to the electrical system of the automobile or apparatus. The socket typically can be inserted into a mating opening in the back of the light assembly so that the bulb is positioned in the assembly at approximately the optical focal point of the light assembly. Unfortunately, regardless of which socket assembly insertion method is used, some light bulbs are damaged severely enough by the insertion process that the final assembled lighting assembly, either initially or soon thereafter, fails to operate. Often this damage involves cracks in the light bulb that allow ambient oxygen to enter the light bulb and oxidize the filament or filaments. Thus, a need exists for a method and apparatus capable of determining whether the light bulb in a lighting assembly will fail, preferably before the lighting assembly is ultimately installed in a larger product, such as an automobile.
Several methods have been developed to determine whether cracks or other leaks are present in the light bulb of a lighting assembly. Window testing is one method known in the art for determining whether a light bulb will fail. The window testing method is generally used to test automotive headlamps. The window testing, an automotive headlamp bulb and socket are connected to a testing device prior to the headlamp bulb and socket""s insertion into an automobile. The testing device comprises a power source for the headlamp bulb and a means for measuring the electrical current through the headlamp bulb. If the current through the headlamp bulb is lower than the normal expected current through the headlamp bulb, then oxidation of the filament may have occurred which signals the pending failure of the light bulb. Generally, if the current through the headlamp is less than approximately ninety percent (90%) of the normal expected current through the headlamp, the light bulb is considered to be unacceptable.
Slope testing is a second method known in the art for determining whether a particular light bulb in an automotive headlamp assembly will fail. In slope testing, an apparatus is used to conduct a three (3) second current test on the headlamp bulb. In this test, the headlamp bulb is connected to a power source and a current measuring device. The headlamp bulb is allowed to warm-up for a period of approximately one and one-half (1.5) seconds. During the next one and one-half (1.5) seconds, the current measuring device measures the current through the headlamp bulb to immediately after the current leaves the headlamp bulb in intervals of one one-hundredth ({fraction (1/100)}) of a second. The slope of these measurements is then calculated. If the slope is negative, the headlamp fails the test. One skilled in the art will appreciate that both the window testing method and the slope testing method may be applied to lighting assemblies other than automotive lighting assemblies.
Generally, automotive lighting assemblies are tested within several hours of the insertion of light bulbs into the socket sub-assemblies and installation of the socket into the lighting assembly. In this time frame, the above-described testing methods will detect large cracks or leaks in the light bulbs, because a large leak will allow enough ambient oxygen to enter the light bulb to affect the window testing results or the slope testing results, even within such a short time after the insertion of the light bulb. However, a problem exists in detecting smaller cracks. Small cracks or leaks do not allow enough ambient oxygen into the light bulb to affect the results of window testing or slope testing for the first forty-eight (48) to seventy-two (72) hours after inserting the light bulb into the apparatus. While one could wait two (2) to three (3) days before testing an automotive lighting sub-assembly, it is impractical to retain the numerous automotive lighting assemblies that may be produced by a manufacturer each day for such time periods to test the function of the light bulbs contained therein. Thus, a need exists for a method and apparatus capable of detecting light bulb leaks immediately after their insertion into lighting sub-assemblies, especially automotive lighting sub-assemblies.
The present invention comprises an apparatus that forces oxygen into cracks or other leaks, if present, in lighting assembly light bulbs, and a method for using the apparatus in detecting such light bulb cracks or leaks. By forcing oxygen under pressure into light bulbs via such cracks or leaks, subsequent window testing or slope testing conducted on a lighting assembly is immediately effective in showing cracks or leaks, even where only very small cracks in the light bulb exist and even when such tests are conducted only a short period of time after the light bulb is inserted into a lighting assembly.
The apparatus comprises a testing assembly having a sealed chamber with a door and a light bulb assembly tray of connected individual testing compartments. Lighting sub-assemblies, comprising a light bulb inserted into an electrical socket sub-assembly, are placed within the individual testing compartments of the light bulb assembly tray, and the light bulb assembly tray is inserted into the sealed chamber. The apparatus further comprises a control assembly having a main control switch and a control panel. The control assembly also comprises an electrical connection board and a gas connection board. Electrical connectors and gas tubes connect the testing assembly to the control assembly.
The sealed chamber is adapted to supply oxygen at a high pressure, provided that such pressure is maintained at a level that will not damage the light bulbs contained within the lighting assemblies. Once the bulbs have been xe2x80x9ccured,xe2x80x9d i.e. pressurized with oxygen for a predetermined period of time, slope testing or window testing currents can be applied to the lighting assemblies to determine if failure is likely.
The testing method of the present invention provides a method of testing for cracks or leaks in light bulbs of lighting assemblies. In practice, the method provides for forcing oxygen into any cracks or leaks in the light bulbs of lighting assemblies, especially automotive lighting assemblies. The oxygen then reacts with light bulb filaments enough to immediately affect the results of subsequently conducted window testing or slope testing of the light bulbs. The testing method of the present invention makes even small leaks in light bulbs immediately detectable after curing. Thus, the number of automotive headlamps that will fail due to cracks or leaks after final assembly in automobiles is greatly reduced. Moreover, the present invention removes any need for a lighting assembly manufacturer to store lighting sub-assemblies for long periods of time to wait for small cracks or leaks to manifest themselves.